The following CSS classes need to be overridden.
.ui-layout-north {
z-index: 20 !important;
overflow: visible !important;
}
.ui-layout-unit-content {
overflow:visible !important;
}
Also in this particular case, the style
attribute of the <span>
tag as shown in the question needs to be modified as follows.
<span style="position: absolute; top:90px; width:1360px; left:0px; bottom:0px;">
Removing the overflow-y: hidden;
attribute (unnecessary) or it won't work even though the above CSS classes have been overridden.